Jim Hill and Holly Wyatt, authors of 'State of Slim: Fix Your Metabolism and Drop 20 Pounds in 8 weeks,' work out together with kettle balls at the Anschutz Health and Wellness Center in Aurora, Colo.

Written by

Nanci Hellmich
USA Today

For years, obesity researchers James Hill and Holly Wyatt have been studying why so many people struggle with losing weight and keeping it off, and the two have concluded that a big part of the problem has to do with lack of physical activity and its impact on metabolism.

"Not everyone agrees with me, but I believe that obesity starts with a lack of movement," says Hill, founding executive director of the Anschutz Health and Wellness Center at the University of Colorado in Denver.

Studies show that when people stop being active, a host of things happen that can lead to weight gain - their ...